U.S. patent application number 15/773761 was filed with the patent office on 2018-11-15 for method of preparing dry hydrogel sheet and dry hydrogel sheet prepared by the same.
This patent application is currently assigned to LOTTE FINE CHEMICAL CO., LTD.. The applicant listed for this patent is LOTTE FINE CHEMICAL CO., LTD.. Invention is credited to Sung Hwan Bang, Kil Seuk Byun, Ji Seon Jeong, Ju Young Jung, Kyong Min Lee, Ju Hee Shin.
Application Number | 20180325244 15/773761 |
Document ID | / |
Family ID | 58662912 |
Filed Date | 2018-11-15 |
United States Patent
Application |
20180325244 |
Kind Code |
A1 |
Jeong; Ji Seon ; et
al. |
November 15, 2018 |
METHOD OF PREPARING DRY HYDROGEL SHEET AND DRY HYDROGEL SHEET
PREPARED BY THE SAME
Abstract
The present invention relates to a method of preparing a dry
hydrogel sheet including the steps of: preparing a cellulose ether
dispersion solution; transferring the dispersion solution to a
coater while maintaining the temperature of the dispersion solution
in the range of a gelation temperature of the dispersion solution
to a boiling point of a dispersion medium; applying the dispersion
solution transferred to the coater as a sheet; preparing a hydrogel
sheet by cooling the applied dispersion solution to induce
gelation; and drying the hydrogel sheet. Since the dry hydrogel
sheet prepared by the method has a low moisture content, it is
possible to ensure the stability of active ingredients, quantify
functional components to be applied to the dry hydrogel sheet, and
ensure the uniformity of the surface appearance and thickness of
the dry hydrogel sheet, which results in the improvement of the
quality of a final product.
Inventors: |
Jeong; Ji Seon; (Incheon,
KR) ; Shin; Ju Hee; (Incheon, KR) ; Bang; Sung
Hwan; (Incheon, KR) ; Jung; Ju Young;
(Incheon, KR) ; Byun; Kil Seuk; (Yongin-Si,
KR) ; Lee; Kyong Min; (Anyang-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LOTTE FINE CHEMICAL CO., LTD. |
Ulsan |
|
KR |
|
|
Assignee: |
LOTTE FINE CHEMICAL CO.,
LTD.
Ulsan
KR
|
Family ID: |
58662912 |
Appl. No.: |
15/773761 |
Filed: |
October 27, 2016 |
PCT Filed: |
October 27, 2016 |
PCT NO: |
PCT/KR2016/012149 |
371 Date: |
May 4, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61K 8/731 20130101;
C08J 2301/28 20130101; C08J 5/18 20130101; A61L 26/008 20130101;
A61K 9/7046 20130101; C08J 3/075 20130101; A61K 9/7007 20130101;
A61L 15/60 20130101; A45D 44/002 20130101; A61L 26/0023 20130101;
A45D 2200/1036 20130101; A45D 2200/1027 20130101; A61L 26/0023
20130101; A61K 8/0212 20130101; A61L 15/28 20130101; A45D 44/22
20130101; C08L 1/26 20130101; A61Q 19/00 20130101; A61K 9/0014
20130101; A61L 15/28 20130101; A45D 37/00 20130101; C08L 1/26
20130101 |
International
Class: |
A45D 44/00 20060101
A45D044/00; A45D 44/22 20060101 A45D044/22; A61K 8/02 20060101
A61K008/02; A61K 9/70 20060101 A61K009/70; C08J 3/075 20060101
C08J003/075; C08J 5/18 20060101 C08J005/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2015 |
KR |
10-2015-0156130 |
Claims
1. A method of preparing a dry hydrogel sheet comprising: preparing
a cellulose ether dispersion solution; transferring the dispersion
solution to a coater while maintaining a temperature of the
dispersion solution in a range from a gelation temperature of the
dispersion solution to a boiling point of a dispersion medium;
applying the dispersion solution transferred to the coater as a
sheet; preparing a hydrogel sheet by cooling the applied dispersion
solution to induce gelation; and drying the hydrogel sheet.
2. The method according to claim 1, further comprising deaerating
the dispersion solution to remove air bubbles from the dispersion
solution.
3. The method according to claim 1, wherein the cellulose ether
dispersion solution includes a cellulose ether, a gelling agent, a
gelling promoter, and a dispersion medium.
4. The method according to claim 3, wherein the cellulose ether is
any one or two or more selected from the group consisting of
hydroxypropyl methyl cellulose, hydroxyethyl cellulose,
hydroxypropyl cellulose, and carboxymethyl cellulose.
5. The method according to claim 1, wherein the coater is selected
from the group consisting of a gravure coater, a comma coater, a
slot-die coater, and a spray coater.
6. The method according to claim 1, wherein a temperature
difference from the gelation temperature of the dispersion solution
to the boiling point of the dispersion medium is within the range
of 50 to 100.degree. C.
7. The method according to claim 1, wherein the cooling of the
dispersion solution is carried out by any one method selected from
natural cooling, cooling with a cooling tunnel, and a combination
thereof.
8. The method according to claim 1, wherein the drying of the
hydrogel sheet is carried out by any one method selected from the
group consisting of hot air drying, infrared drying, and microwave
drying, or a combination of two or more thereof.
9. A dry hydrogel sheet prepared by the method according to claim
1.
10. The dry hydrogel sheet according to claim 9, which has a
thickness of 10 to 200 .mu.m.
11. A cosmetic mask pack comprising the dry hydrogel sheet
according to claim 9.
12. A medical patch comprising the dry hydrogel sheet according to
claim 9.
13. A dry hydrogel sheet prepared by the method according to claim
2.
14. A dry hydrogel sheet prepared by the method according to claim
3.
15. A dry hydrogel sheet prepared by the method according to claim
4.
16. A dry hydrogel sheet prepared by the method according to claim
5.
17. A dry hydrogel sheet prepared by the method according to claim
6.
18. A dry hydrogel sheet prepared by the method according to claim
7.
19. A dry hydrogel sheet prepared by the method according to claim
8.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of preparing a dry
hydrogel sheet and a dry hydrogel sheet prepared by the same.
BACKGROUND ART
[0002] A hydrogel is a network of hydrophilic polymer chains in
which water is the dispersion medium. The hydrogel is not dissolved
but swelled in water so that it can contain a large amount of water
in the structure thereof and thus it possesses a degree of
flexibility very similar to that of natural tissue.
[0003] The hydrogel has been used in the medical and pharmaceutical
field, such as the fields of tissue engineering, cell culture,
sustained-release drug delivery systems, biosensors, soft lenses,
medical electrodes, and the like, due to its unique hydrophilicity
and flexibility, and has also been applied in various fields
including absorbents for hygienic goods, delivery media of cosmetic
agents, and the like.
[0004] As the conventional technologies using the hydrogel, Patent
Document 1 (Korean Laid-Open Patent Publication No.
10-2014-0108803) discloses a method of preparing a hydrogel film,
which includes preparing a resin for a hydrogel; forming a hydrogel
by applying the resin for a hydrogel onto a surface of a release
film and then drying the same; and crosslinking and swelling the
hydrogel by infiltrating the hydrogel formed on the surface of a
release film with a crosslinking-swelling agent. In this case, the
resin for a hydrogel includes 1 to 40 wt % of a polymer resin
containing one or more selected from a water-soluble polymer and a
natural polymer, 0.05 to 20 wt % of sodium alginate, 0.1 to 20 wt %
of a plasticizer, 0.1 to 20 wt % of a moisturizer, and 20 to 98 wt
% of distilled water. Regarding Patent Document 1, it is described
that a hydrogel film having excellent mechanical strength, good
flexibility, excellent adhesion to skin, excellent comfort, and the
like may be provided.
[0005] In addition, Patent Document 2 (Korean Registered Patent No.
10-1563325) discloses a method of preparing an antipyretic patch,
which includes applying an adhesive onto one surface of an urethane
film and then adhering a nonwoven fabric thereto; mixing a hydrogel
with a functional material having antipyretic efficacy to prepare a
functional hydrogel; applying the functional hydrogel onto a
surface of the nonwoven fabric or one surface of a release film and
then bringing the functional hydrogel in close contact with the
nonwoven fabric or the release film in such a way that the
functional hydrogel is positioned between the nonwoven fabric and
the release film to prepare a patch sheet; thermally treating and
drying the patch sheet to form a semisolid-phase functional
hydrogel from the functional hydrogel; and cutting the patch sheet
including the semisolid-phase functional hydrogel into a shape
conforming with an application site of the human body. In this
case, the hydrogel includes 5 to 15 wt % of polyacrylic acid, 10 to
40 wt % of glycerin, 1 to 10 wt % of sodium hydroxide, 0.1 to 3 wt
% of agar, 0.1 to 3 wt % of Polysorbate 60, and water as the
remainder, and the functional material is prepared by mixing a
functional mixture comprising any one of menthoxypropanediol,
menthyl lactate and mixture thereof; and oriental plant extracts
comprising two or more selected from a cucumber extract, an aloe
extract, a Tricholoma matsutake extract, a Phellodendron amurense
bark extract, a carrot root extract, and a Lycium chinense fruit
extract. The hydrogel and the functional material are mixed in a
ratio of 97 to 99 wt % and 1 to 3 wt %, respectively. Patent
Document 2 describes that when the antipyretic patch prepared by
the above method is applied to a corresponding site in the human
body, fever may be effectively reduced.
[0006] However, when a functional component is applied to a
hydrogel as prior-art documents, the concentration of an active
ingredient may be diluted or the stability of an active ingredient
may be adversely affected within the shelf life of a product. For
example, since the hydrogel has a high moisture content,
decomposition caused by proliferation of microorganisms may occur,
and high distribution costs are also required.
PRIOR-ART DOCUMENTS
Patent Documents
[0007] (Patent Document 1) KR1020140108803 A
[0008] (Patent Document 2) KR101563325 B
DISCLOSURE
Technical Problem
[0009] It is an object of the present invention to provide a method
of preparing a dry hydrogel sheet which is capable of solving a
problem of a conventional hydrogel such as decomposition caused by
proliferation of microorganisms occurring due to a high moisture
content by lowering a moisture content, and to which a quantified
amount of functional component can be applied.
[0010] It is another object of the present invention to provide a
method of preparing a dry hydrogel sheet which has a uniform
surface appearance and ensures the uniformity of a thickness by
adjusting the temperature of a dispersion solution.
[0011] It is still another object of the present invention to
provide a dry hydrogel sheet prepared by the above-described
method.
Technical Solution
[0012] The present invention is designed to achieve the above
objects and provides a method of preparing a dry hydrogel sheet,
which includes preparing a cellulose ether dispersion solution;
transferring the dispersion solution to a coater while maintaining
a temperature of the dispersion solution in a range of a gelation
temperature of the dispersion solution to a boiling point of a
dispersion medium; applying the dispersion solution transferred to
the coater as a sheet; preparing a hydrogel sheet by cooling the
applied dispersion solution to induce gelation; and drying the
hydrogel sheet.
[0013] The method may further include deaerating the dispersion
solution to remove air bubbles from the dispersion solution.
[0014] The cellulose ether dispersion solution may include a
cellulose ether, a gelling agent, a gelling promoter, and a
dispersion medium. The cellulose ether may be any one or two or
more selected from the group consisting of hydroxypropyl methyl
cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and
carboxymethyl cellulose.
[0015] The coater may be selected from the group consisting of a
gravure coater, a comma coater, a slot-die coater, and a spray
coater.
[0016] It is preferable that the temperature ranging from a
gelation temperature of the dispersion solution to a boiling point
of the dispersion medium is 50 to 100.degree. C.
[0017] The cooling of the dispersion solution may be carried out by
any one method selected from natural cooling, cooling with a
cooling tunnel, and a combination thereof. The drying of the
hydrogel sheet may be carried out by any one method selected from
the group consisting of hot air drying, infrared drying, and
microwave drying, or a combination of two or more thereof.
[0018] In addition, the present invention provides a dry hydrogel
sheet prepared by the above-described method. In this case, it is
preferable that the sheet has a thickness of 10 to 200 .mu.m.
[0019] Additionally, the present invention provides a cosmetic mask
pack or a medical patch including the dry hydrogel sheet.
Advantageous Effects
[0020] A dry hydrogel sheet prepared by the method according to the
present invention has a low moisture content and thus can solve a
problem of a conventional hydrogel such as decomposition caused by
proliferation of microorganisms occurring due to a high moisture
content. Also, the volume and weight of the hydrogel sheet
significantly decrease so that distribution costs can be
reduced.
[0021] In addition, a quantified amount of functional component can
be applied to the dry hydrogel sheet so that a problem of a
conventional hydrogel sheet, such as a concentration dilution of an
active ingredient occurring when a functional component is applied
to the hydrogel sheet, can be solved.
[0022] Additionally, the uniformity of the surface and thickness of
the dry hydrogel sheet can be ensured by appropriately adjusting
the temperature of a cellulose ether dispersion solution so that
the quality of a final product can be improved.
DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is an image of a dry hydrogel sheet prepared
according to the Example.
[0024] FIG. 2 is an image of a dry hydrogel sheet prepared
according to the Comparative Example.
[0025] FIG. 3 is an image obtained by photographing the dry
hydrogel sheet of FIG. 1, which is placed on the word
"Hydrogel".
[0026] FIG. 4 is an image obtained by photographing the dry
hydrogel sheet of FIG. 2, which is placed on the word
"Hydrogel".
[0027] FIG. 5 is a set of images showing a dry hydrogel sheet
(left) and the same hydrogel sheet gelated due to applied moisture
(right).
MODES OF THE INVENTION
[0028] The present invention relates to a method of preparing a dry
hydrogel sheet and a dry hydrogel sheet prepared by the same.
[0029] First, the method of preparing a dry hydrogel sheet will be
described. The method includes preparing a cellulose ether
dispersion solution; transferring the dispersion solution to a
coater while maintaining a temperature of the dispersion solution
in a range of a gelation temperature of the dispersion solution to
a boiling point of a dispersion medium; applying the transferred
dispersion solution as a sheet; preparing a hydrogel sheet by
cooling the applied dispersion solution to induce gelation; and
drying the hydrogel sheet.
[0030] Hereinafter, the method of preparing a dry hydrogel sheet
according to one embodiment of the present invention will be
described in detail.
[0031] (1) Preparation of Dispersion Solution
[0032] In this step, a cellulose ether dispersion solution is
prepared. The cellulose ether dispersion solution may include a
cellulose ether, a gelling agent, a gelling promoter, and a
dispersion medium. The preparation of the cellulose ether
dispersion solution may include preparing a preliminary mixture by
mixing a cellulose ether, a gelling agent, and a gelling promoter;
and dispersing the preliminary mixture in a dispersion medium.
[0033] The method of preparing a dry hydrogel sheet according to
the present invention may further include deaerating the dispersion
solution to remove air bubbles from the dispersion solution. The
deaeration is carried out preferably at 55 to 65.degree. C. for 20
to 60 minutes. When a preliminary mixture is prepared and then
dispersed in a dispersion medium as described above, a process time
required to carry out the deaeration may be shortened compared to
when a cellulose ether, a gelling agent, and a gelling promoter are
dispersed in a dispersion medium one at a time.
[0034] The cellulose ether refers to a cellulose derivative
produced by etherifying the hydroxyl groups of cellulose. The
properties of cellulose ether are water-soluble and swelled after
absorbing water. As the cellulose ether, any one or two or more
selected from the group consisting of hydroxypropyl methyl
cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and
carboxymethyl cellulose may be used, and preferably, hydroxypropyl
methyl cellulose is used.
[0035] The gelling agent is used to form a gel, adjust strength,
control syneresis, and improve comfort, and a natural polymer may
be used rather than a water-soluble synthetic polymer in
consideration of skin toxicity. As the natural polymer, any one or
two or more selected from the group consisting of carrageenan,
locust bean gum, mannose, and water-chestnut flour may be used.
[0036] The gelling promoter serves to crosslink the natural
polymer. The gelling promoter may be a Group 1 or 2 metal salt, and
for example, any one or two or more selected from the group
consisting of magnesium chloride, potassium chloride, calcium
chloride, and sodium chloride may be used.
[0037] The dispersion medium may be water, more preferably,
85.degree. C. or more hot water.
[0038] (2) Transference of Dispersion Solution
[0039] In this step, the dispersion solution is transferred to a
coater while maintaining the temperature of the dispersion solution
in a range of a gelation temperature of the dispersion solution to
a boiling point of the dispersion medium.
[0040] In the preparation of the dry hydrogel sheet according to
the present invention, it is very important to adjust the
temperature of the cellulose ether dispersion solution. When the
temperature of the dispersion solution is less than the gelation
temperature thereof, gelation proceeds during a transference
process to cause a non-uniform concentration of solids, resulting
in adverse effects on surface characteristics of a final film. On
the other hand, when the temperature of the dispersion solution is
greater than the boiling point of the dispersion medium, the
dispersion medium is evaporated to cause a change in a
concentration, and thus a uniform product may not be obtained. In
consideration of the above problems, a temperature ranging from a
gelation temperature of the dispersion solution to a boiling point
of the dispersion medium is preferably 50 to 100.degree. C., more
preferably, 55 to 90.degree. C.
[0041] Specifically, FIG. 1 illustrates an image of a dry hydrogel
sheet when the temperature of a cellulose ether dispersion solution
is maintained within the above range. It can be seen through FIG. 1
that a dry hydrogel sheet prepared under this condition has a
uniform surface appearance. On the other hand, FIG. 2 illustrates
an image of a dry hydrogel sheet when the temperature of a
dispersion solution is out of the above range. It can be seen
through FIG. 2 that a dry hydrogel sheet prepared under this
condition has a non-uniform and rough surface appearance.
[0042] As the coater, a coater commonly used in the related art may
be used without limitation. For example, the coater may be selected
from the group consisting of a gravure coater, a comma coater, a
slot-die coater, and a spray coater.
[0043] (3) Application of Dispersion Solution
[0044] In this step, the dispersion solution transferred to the
coater is applied as a sheet. The dispersion solution may be
applied onto a release paper, and the dispersion solution thus
applied preferably has a thickness of 0.1 to 10 mm. The thickness
of the dispersion solution affects a thickness of a dry hydrogel
sheet, which is a final product, after being impregnated with
water, i.e., a thickness of a hydrogel sheet to be applied to the
skin. That is, when the thickness of the dispersion solution is
less than 0.1 mm, a hydrogel sheet to be applied to the skin may be
torn due to reduced strength. On the other hand, when the thickness
the dispersion solution is greater than 10 mm, adhesion of a
hydrogel sheet to skin may be significantly reduced, and efficiency
of releasing active ingredients may also be degraded.
[0045] (4) Preparation of Hydrogel Sheet
[0046] In this step, the dispersion solution applied according to
the step (3) is cooled and gelated to prepare a hydrogel sheet.
[0047] In this case, the cooling of the dispersion solution may be
carried out by any one method selected from natural cooling,
cooling with a cooling tunnel, and a combination thereof.
[0048] (5) Drying of Hydrogel Sheet
[0049] In this step, the hydrogel sheet prepared according to the
step (4) is dried to prepare a dry hydrogel sheet as a final
product.
[0050] In this case, the drying of the hydrogel sheet may be
carried out by any one method selected from the group consisting of
hot air drying, infrared drying, and microwave drying, or a
combination of two or more thereof. For example, when a hot air
drying method is used, the drying process may be carried out at 120
to 180.degree. C. for 1 to 60 minutes.
[0051] In addition, the present invention provides a dry hydrogel
sheet prepared according to the above-described method.
[0052] The dry hydrogel sheet exhibits a reversible property in
which it is gelated when impregnated with water. Therefore, for
practically applying the dry hydrogel sheet to the skin, a subject
uses the dry hydrogel sheet after impregnation with a liquid
containing functional components. Through this process, the dry
hydrogel sheet is gelated and thus may be used as a common hydrogel
sheet in a gel state. Specifically, FIG. 5 is a set of images
showing a dry hydrogel sheet (left) and the same hydrogel sheet
gelated due to applied moisture (right).
[0053] The dry hydrogel sheet preferably has a thickness of 10 to
200 .mu.m. When the thickness of the dry hydrogel sheet is less
than 10 .mu.m, the thickness of the hydrogel sheet in a gel state
becomes thinner so that it may be torn due to reduced strength. On
the other hand, when the thickness of the dry hydrogel sheet is
greater than 200 .mu.m, adhesion of a hydrogel sheet in a gel state
to skin may be significantly reduced, and efficiency of releasing
active ingredients may also be degraded.
[0054] In the case of a conventional hydrogel sheet, there is a
problem of dilution of the concentration of an active ingredient
occurring when a functional component is applied to the hydrogel
sheet. On the other hand, in the case of the dry hydrogel sheet
according to the present invention, a quantified amount of
functional component may be applied. The dry hydrogel sheet has a
low moisture content and thus a problem of decomposition caused by
proliferation of microorganisms occurring due to a high moisture
content can be solved. Also, the volume and weight of the hydrogel
sheet significantly decrease so that distribution costs can be
reduced.
[0055] In addition, the present invention provides a cosmetic mask
pack or a medical patch including the dry hydrogel sheet. However,
the use of the dry hydrogel sheet is not limited to the above
applications, and the dry hydrogel sheet may be widely applied to
various products in the fields such as tissue engineering, cell
culture, biosensors, soft lenses, medical electrodes, absorbents
for hygienic goods, and the like.
[0056] Hereinafter, the present invention will be described in more
detail with reference to examples of the present invention.
However, the present invention is not limited by the following
examples.
EXAMPLE
[0057] Hydroxypropyl methyl cellulose (HPMC; HPMC 2910 commercially
available from Lotte Fine Chemical Co., Ltd.), carrageenan, and
potassium chloride (KCl) were mixed at a ratio of 0.3 mole of
carrageenan and 0.07 mole of KCl per 1 mole of a glucose unit of
HPMC to prepare a preliminary mixture
(HPMC:carrageenan:KCl=1:0.3:0.07). Subsequently, the preliminary
mixture was dispersed at a solid concentration of 5 wt % in
85.degree. C. hot water (a gelation temperature of the preliminary
mixture is 45.degree. C.), and then maintained at 60.degree. C.
until all air bubbles in the dispersion solution were removed.
[0058] The dispersion solution from which air bubbles were removed
was transferred to a coater (comma-coater) set to 70.degree. C.
[0059] The dispersion solution transferred to the coater was
transferred to a coating solution supply unit and applied as a
sheet on a release paper. In this case, the dispersion solution was
applied with a thickness of 0.2 mm.
[0060] The dispersion solution applied on the release paper was
naturally cooled and gelated to prepare a hydrogel sheet during a
transference process.
[0061] The hydrogel sheet was dried using a hot air dryer at
170.degree. C. for 4 minutes to prepare a dry hydrogel sheet.
Comparative Example
[0062] A dry hydrogel sheet was prepared in the same manner as in
the example except that the dispersion solution from which air
bubbles were removed was transferred to a coater set to 40.degree.
C.
[0063] <Evaluation Method>
[0064] Thickness of Dry Hydrogel Sheet
[0065] The thicknesses of dry hydrogel sheets with a size of
300.times.300 mm according to the example and the comparative
example were measured using a thickness gauge (No. 547-401
commercially available from Mitutoyo). In this case, the
thicknesses at 15 points randomly selected in the dry hydrogel
sheet were measured. The thickness measured at each point and the
average and standard deviation thereof are shown in the following
Table 1.
TABLE-US-00001 TABLE 1 Point No. Comparative Example (.mu.m)
Example (.mu.m) 1 36 32 2 23 31 3 42 33 4 45 31 5 37 32 6 46 34 7
37 32 8 36 31 9 38 31 10 36 32 11 37 31 12 35 34 13 27 32 14 5 36
15 9 34 Average 32.6 32.4 Standard deviation 11.9 1.5
[0066] As shown in Table 1, it can be seen that the dry hydrogel
sheet according to the present invention had an average thickness
similar to that of a dry hydrogel sheet according to the
comparative example, but exhibited a significantly lower standard
deviation compared to a dry hydrogel sheet according to the
comparative example. Accordingly, it can be confirmed that a dry
hydrogel sheet with a uniform thickness distribution can be
prepared according to the method of the present invention.
[0067] In addition, when FIGS. 1 and 2 illustrating images of dry
hydrogel sheets according to the example and the comparative
example are compared, it can also be confirmed from their
appearances that the dry hydrogel sheet according to the example
had a more uniform surface than a dry hydrogel sheet according to
the comparative example. Also, FIGS. 3 and 4 are images obtained by
photographing the dry hydrogel sheets of FIGS. 1 and 2 placed on
the word "Hydrogel". It can be confirmed through FIGS. 3 and 4 that
in the case of the dry hydrogel sheet according to the example, the
word was uniformly seen through the sheet, whereas in the case of a
dry hydrogel sheet according to the comparative example, the word
was not uniformly seen through the sheet. This proves that the
hydrogel in a dry hydrogel sheet according to the comparative
example is not uniformly distributed.
[0068] The examples disclosed in the present invention are intended
to illustrate, not limit, the technical spirit of the present
invention, and the scope of the present invention should be
interpreted by the appended claims and to encompass all equivalents
falling within the scope of present invention.
* * * * *